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Cape Town - Finding life beyond Earth may be related to clues about whether life has more than origin here on Earth, an expert has said.

Professor Paul Davies said that during his long career, scientists have gradually come to accept that life may exist elsewhere in the universe.

In 2005, he took up the chair of the Seti (Search for Extraterrestrial Intelligence): Post-Detection Science and Technology Taskgroup of the International Academy of Astronautics.

He said speculation that finding many planets means that life is abundant in the universe is flawed.

"Maybe we like the idea of the universe teaming with life, I do. How can we test it? If we don't know what the mechanism of life's origin was, is there any other way we can test short of finding ET?"

Evidence

According to Davies, the way to test whether life could originate in the universe was to test to see whether different forms of life originated on Earth.

"If life pops up readily in Earth-like conditions, surely it should have started many times right here on Earth. Because after all, no planet is more Earth-like than Earth," he said.

Recently, the journal Cosmology published findings from Nasa scientist Richard Hoover that evidence for microbes was found in a meteorite.

Nasa distanced itself from the findings and they remain contentious in the scientific community.

"All known life on Earth is descended from a common ancestor. We're all on the same tree. But we don't know all life on Earth.

"Almost all life on Earth is microbial... and in the microbial realm only a tiny tiny fraction of these organisms have been characterised, let alone cultured or sequenced," Davies said.

He added that current technology allowed for screening of life as we know it, but would have difficulty when presented with life as we don't know it.

'Shadow biosphere'

"When you talk to molecular biologists, they decide on identification procedures that are customised to life as we know it.

"If we're talking about a different form of life, with a different biochemistry and a different biology - a different tree of life altogether with a separate origin, starting from scratch independently, we don't know what to look for; the customised tests won't work."

Davies, who is a proponent of panspermia - the theory that life is distributed widely in the universe and via impacts with comets or meteors - said that alien life forms may possibly be found on Earth.

"There could be some shadow biosphere on Earth - I say aliens under our noses. The term 'alien' has been subtly redefined because of this.

"You may not think of alien as necessarily being from space, though it may be. Our life may have come from space. There's a case that life may well have started on Mars and come here with material ejected from Mars via comet impact.

"The question is: Are there any aliens under our noses or even in our noses? How would we know? The truth is that we don't know."Alien life

Many scientists are searching for alternative life forms on Earth and despite finding a variety of organisms that defy convention, experts have yet to find a life form that can truly be described as "alien".

If researchers were able to find a unique form of life, it would lend credibility to the idea that the universe is teaming with life, said Davies, who has an asteroid, 6870 Pauldavies, named after him.

"If we just found one microbe, one single representative sample... that was so different from known life, it could not possibly have had a common origin, that would establish that life does arise readily and therefore will surely arise on Earth-like planets all around the universe.

"Because it would be remarkable if among all the Earth-like planets in the universe, life would have started twice on one, and not on all the others."

Davies, a professor at Arizona State University, has had a career in theoretical physics, cosmology and astrobiology, and has authored several books, from The Physics of Time Asymmetry in 1974 to, most recently, The Eerie Silence.

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